US7463233B2 - Ferroelectric liquid crystal display and method of driving the same - Google Patents
Ferroelectric liquid crystal display and method of driving the same Download PDFInfo
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- US7463233B2 US7463233B2 US10/603,763 US60376303A US7463233B2 US 7463233 B2 US7463233 B2 US 7463233B2 US 60376303 A US60376303 A US 60376303A US 7463233 B2 US7463233 B2 US 7463233B2
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
- G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
- G09G3/3611—Control of matrices with row and column drivers
- G09G3/3648—Control of matrices with row and column drivers using an active matrix
- G09G3/3651—Control of matrices with row and column drivers using an active matrix using multistable liquid crystals, e.g. ferroelectric liquid crystals
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2310/00—Command of the display device
- G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/02—Improving the quality of display appearance
- G09G2320/0261—Improving the quality of display appearance in the context of movement of objects on the screen or movement of the observer relative to the screen
Definitions
- the present invention relates to ferroelectric liquid crystal displays (LCDs), and more particularly to a ferroelectric LCD and a method of driving the same according to an impulse-type method wherein a voltage holding ratio (VHR) of liquid crystal cells is reduced.
- VHR voltage holding ratio
- LCDs display pictures by applying electric fields to a layer of liquid crystal material in response to an applied video signal, wherein the applied electric field controls the orientation liquid crystal molecules within the layer of liquid crystal material and therefore the light transmittance characteristics of the liquid crystal material.
- FIG. 1 illustrates a related art active matrix LCD (AM-LCD).
- related art AM-LCDs generally include an LCD panel formed of lower and upper substrates.
- the lower substrate i.e., the TFT array substrate
- the TFT array substrate supports a plurality of data lines D 1 to Dm and a plurality of gate lines G 1 to Gn arranged to cross each other.
- Liquid crystal cells (Clc) are defined by, and thin film transistors (TFTs) are formed at, the crossings of the gate and data lines, wherein the TFTs are provided for driving corresponding ones of liquid crystal cells.
- a linear polarization filter having a first polarization axis is mounted onto the rear surface of the TFT array substrate.
- a protecting film is formed over the entire front surface of the TFT array substrate in order to cover the TFTs and the gate and data lines.
- An alignment film is formed over the entire surface of the protecting film. Alignment grooves are formed in the alignment film for aligning subsequently provided liquid crystal material.
- the front surface of the upper substrate i.e., the color filter substrate
- the rear surface of the color filter substrate supports a polarization plate.
- the upper and lower substrates are bonded together by a sealant and liquid crystal material is injected between the bonded substrates.
- Storage capacitors (Cst) are connected to corresponding ones of the liquid crystal cells (Clc) and allow each liquid crystal cell (Clc) to maintain an applied data voltage.
- Storage capacitors (Cst) of each liquid crystal cell (Clc) include an electrode connected to one portion of a corresponding pixel electrode and another electrode connected to a preceding one of the gate line G 1 to Gn- 1 .
- Gate electrodes of each TFT are connected to the gate lines G 1 to Gn that transmit scan pulses.
- Source electrodes of each TFT are connected to the data lines D 1 to Dm that transmit data voltages.
- Drain electrodes of each TFT are connected to respective ones of the pixel electrodes within the liquid crystal cell (Clc).
- the black matrix is formed in boundary regions between adjacent liquid crystal cells (Clc) and in TFT regions of each liquid crystal cell (Clc) to absorb incident light and prevent light transmitted though portions of the liquid crystal material between adjacent liquid crystal cells, having undesirable optical properties, from being displayed by the LCD.
- the color filter selectively transmits light having predetermined wavelength ranges corresponding to red, green, and blue colors.
- LCD display pictures by sequentially applying scan pulses SP 1 to SPn to the gate lines G 1 to Gn.
- Horizontal lines of liquid crystal cells connected to gate lines having scan pulses applied to them e.g., having selected gate lines
- scan pulses SP 1 to SPn are generated using a shift register having stages ST 1 to STn electrically connected to corresponding ones of the gate lines G 1 to Gn, respectively.
- the first stage (ST 1 ) of the shift register generates a scan pulse (SP 1 ) in synchrony with a gate start pulse (GSP) outputted from a timing controller (not shown).
- the second to nth stages ST 2 to STn sequentially generate scan pulses SP 2 to SPn, respectively, in response to preceding ones of the scan pulses SP 1 to SPn- 1 , respectively, supplied from the preceding stage.
- a gate shift clock (GSC) signal and a gate output enable (GOE) signal control the output timing of the scan pulses.
- the scan pulses SP 1 to SPn are sequentially applied to the first gate line to the nth gate line G 1 to Gn in response to the generated gate start pulse (GSP).
- GSP gate start pulse
- Each scan pulse SP 1 to SPn is applied to a corresponding gate line G 1 to Gn once during one frame period of the LCD panel.
- liquid crystal material within LCDs exhibits an intermediate material phase between solid and liquid phases wherein liquid crystal molecules exhibit both fluidity and elasticity.
- liquid crystal material used in LCDs include twisted nematic mode (TN mode) liquid crystal material.
- a high logic voltage (Vgh) of each scan pulse (SP) is greater than a threshold voltage of a TFT and forms a conductive channel between the source/drain electrodes of the TFT such that liquid crystal cells of TN mode LCDs become charged with a voltage (Vlc). Accordingly, the liquid crystal cell substantially maintains the charged voltage during the entire frame period of the LCD panel.
- a low logic voltage (Vgl) of the scan pulse (SP) is lower than the threshold voltage of the TFT.
- a voltage holding ratio (VHR) of each liquid crystal cell is the difference between a peak data voltage (Vdata) of the data voltage applied to the liquid crystal cell and an average voltage (Vavrg) of voltage actually charged by the liquid crystal cell when the peak data voltage (Vdata) is applied.
- VHR voltage holding ratio
- Vavrg average voltage
- TN mode liquid crystal material has a relatively low response speed and a relatively narrow viewing angle.
- FLC ferroelectric liquid crystal
- FLC material exhibits a lamellar structure, wherein each layer of FLC material has the same electric and magnetic properties. Accordingly, when FLC material is driven, molecules of FLC material within the same layer spontaneously rotate (i.e., polarize) along a virtual cone in response to an applied electric field. In the absence of an applied electric field, molecules within the FLC material spontaneously polarize to an original alignment orientation.
- FLC material when external electric fields are applied to the FLC material, molecules within the FLC material rotate rapidly by interaction of an external field and exhibit spontaneous polarization.
- the response speed of FLC material is typically between a hundred or a thousand times faster than other modes of liquid crystal material.
- FLC material has an inherent in-plane-switching property and can therefore be used to provide LCDs with wide viewing angles without special electrode structures or compensation films.
- FLC material has an inherent in-plane-switching property and can therefore be used to provide LCDs with wide viewing angles without special electrode structures or compensation films.
- FLC material may be classified as V-Switching or Half V-Switching Modes.
- V-Switching Mode FLC material exhibits the following thermodynamic phase transformations upon decreasing temperature: isotropic ⁇ smectic A phase (SA) ⁇ smectic X phase (Sm X*) ⁇ crystalline.
- SA smectic A phase
- Sm X* smectic X phase
- FIG. 5 illustrates a graph of transmissivity of incident light versus voltage applied to a V-Switching Mode ferroelectric liquid crystal cell.
- V-Switching Mode FLC material beneficially has high response speed and wide viewing angle characteristics but disadvantageously requires a large amount of power in order to be driven because a capacitance value of the V-Switching Mode FLC material is relatively large. Therefore, a capacitance value of a storage capacitor used to maintain applied data voltages are also be large. Accordingly, if V-Switching Mode FLC material is used LCDs, an aperture ratio of the LCD becomes low since the power consumption of LCD and an electrode area of a sub-capacitor increases.
- Half V-Switching Mode FLC material beneficially has a high response speed and wide viewing angle characteristics and further has a relatively low capacitance value. Therefore, Half V-Switching Mode FLC material is often used to display moving pictures.
- FIG. 6 illustrates phase transformations of Half V-Switching Mode ferroelectric liquid crystal material.
- Half V-Switching Mode FLC material upon decreasing temperature below the phase transformation temperature (Tni), Half V-Switching Mode FLC material exhibits a phase transformation from the isotropic to the nematic phase (N*), below phase transformation temperature (Tsn), the Half V-Switching Mode FLC material exhibits a phase transformation from the nematic phase (N*) to the smectic C phase (Sm C*), and below phase transformation temperature (Tcs) the Half V-Switching Mode FLC material exhibits a phase transformation from the smectic C phase to the crystalline phase. Therefore, as the temperature decreases, Half V-Switching Mode FLC material exhibits the following thermodynamic phase transformations: isotropic ⁇ nematic (N*) ⁇ smectic C phase (Sm C*) ⁇ crystalline.
- FIG. 7 illustrates the fabrication of a liquid crystal cell including Half V-Switching Mode FLC material.
- Half V-Switching Mode FLC material is typically injected into a liquid crystal cell at a temperature above Tni. Accordingly, upon being injected into the liquid crystal cell, molecules within the FLC material are oriented and distributed substantially isotropically (e.g., randomly). Upon lowering the temperature of the FLC material below Tni, molecules within the FLC material become aligned substantially parallel to each other along a direction dictated by the rubbing direction of an orientation layer and the FLC material exhibits the nematic phase (N*).
- the FLC material If the temperature of the FLC material is further lowered the temperature below Tsn in the presence of an electric field, the FLC material exhibits the smectic phase (C*) and the liquid crystal molecules spontaneously polarize along the direction of the applied electric field to exhibit a monostable state, wherein liquid crystal molecules uniformly assume one of two possible molecular arrangements. If, on the other hand, the temperature of the FLC material is lowered below Tsn in the absence of the applied electric field, the liquid crystal molecules become separated into layers to exhibit a bistable state, wherein liquid crystal molecules within each layer uniformly assume one of the two possible molecular arrangements. Further, the distribution of the molecular arrangements within the layers is substantially random.
- the Half V-Mode FLC cells are generally fabricated to exhibit the monostable state by cooling the FLC material below Tsn in the presence of an electric filed generated by applying a small direct current (DC) voltage to the LCD panel.
- DC direct current
- the symbol “ ” describes the direction of the applied electric field as extending out of the plane of the illustration. Therefore the spontaneous polarization direction of the FLC material also extends out of the plane of the illustration. Accordingly, electrodes used to generate the applied electric field are formed on upper and lower plates of the liquid crystal cell, extending out of the plane of the illustration. Further, the orientation layer described above is formed on the upper and lower plates.
- FIGS. 8A and 8B illustrate the dependence of light transmissivity on a voltage applied to a Half V-Switching Mode FLC cell.
- Half V-Switching Mode FLC cells containing FLC material aligned in the presence of an applied electric field generated by a voltage having a negative polarity ( ⁇ V) (i.e., fabricated in the presence of an electric field having a negative polarity), transmit light in the presence of an applied voltage having a positive polarity (+V) by rotating a polarization axis of the light by 90°.
- the light transmissivity of the Half V-Switching Mode FLC cell increases proportionally to the intensity of an applied positive electric field generated by the positive voltage (+V).
- the light transmissivity of the Half V-Switching Mode FLC cell attains a maximum value when the intensity of the applied positive electric field is greater than a fixed threshold value of the FLC material.
- the Half V-Switching Mode FLC cell In the presence of an applied voltage having a negative voltage ( ⁇ V), the Half V-Switching Mode FLC cell does not rotate the polarization axis of the light. Accordingly, in the presence of an applied voltage having a negative polarity, the Half V-Switching Mode FLC cell transmits substantially no light (i.e., the Half V-Switching Mode FLC cell intercepts the light).
- Half V-Switching Mode FLC cells containing FLC material aligned in the presence of an applied electric field generated by a voltage having a positive polarity (+V) (i.e., fabricated in the presence of an electric field having a positive polarity), transmit light in the presence of an applied voltage having a negative polarity ( ⁇ V).
- ⁇ V negative polarity
- the Half V-Switching Mode FLC cell does not rotate the polarization axis of the light. Accordingly, in the presence of an applied voltage having a positive polarity, the Half V-Switching Mode FLC cell intercepts the light.
- FIGS. 9A and 9B illustrate the orientation directions of Half V-Switching Mode FLC material in the presence of applied electric fields used to fabricate the liquid crystal cell and applied electric fields used to drive the liquid crystal cell, respectively.
- an electric field having a positive polarity e.g., an electric field generated by applying a voltage having a positive polarity to the LCD panel
- E(+) an electric field generated by applying a voltage having a positive polarity to the LCD panel
- Ps spontaneous polarization direction
- a polarization state of light incident to a lower plate of the LCD panel may be rotated to substantially align with the polarization direction of an upper polarizer on an upper plate via the FLC material, having the spontaneous polarization direction (Ps) uniformly aligned with the externally applied electric field having the positive polarity, and the incident light is transmitted through the upper plate.
- Ps spontaneous polarization direction
- the applied external electric field is generated by an applied voltage having a negative polarity (and thus itself has a negative polarity (E( ⁇ ))
- the FLC material remains uniformly aligned along its initial spontaneous polarization direction (Ps) (characterized by the applied electric field having the negative polarity) and the incident light beam is not transmitted through the upper plate (i.e., the light is intercepted by the liquid crystal cell).
- the brightness of the Half V-Switching Mode FLC cell described above is relatively low and cannot precisely express images consistent with received video signals because the average voltage (Vavrg) charged within each liquid crystal cell is low and the voltage holding ratio (VHR) is excessively large. More specifically, the Half V-Switching Mode FLC cell immediately discharges the charged voltage after the peak data voltage (Vdata) is charged when the scan pulse (SP) attains the high logic voltage (Vgh).
- the liquid crystal cell cannot effectively express gray scale values of expressed images consistent with the received video signal and the brightness becomes much reduced compared to the brightness required by the received video signal when the voltage of the Half V-Switching Mode FLC cell drops abruptly as described above because the average voltage (Vavrg) of the liquid crystal cell becomes much smaller than the peak voltage of the data voltage (Vdata).
- defects may be generated within the fabricated Half V-Switching Mode FLC cell when the LCD panel is driven according to an inversion driving method.
- defects may be manifested by the lowering of a brightness of displayed pictures and flickering (e.g., blinking) of the displayed pictures.
- flickering may be reduced by employing inversion driving methods to drive LCD panels, wherein the inversion driving methods also prevent a degradation of liquid crystal material within the LCD panel by inverting the polarity of applied data voltages between predetermined periods of the LCD panel.
- a frame inversion driving method inverts the polarity of data voltages applied between successive frame periods at a frequency of 60 Hz, in correspondence with the frame period of 16.7 ms.
- a line inversion driving method inverts the polarity of data voltages between successive frame periods and horizontal lines.
- a column inversion driving method inverts the polarity of data voltages between successive frame periods and vertical lines.
- a dot inversion driving method inverts the polarity of data voltages between successive frame periods, horizontal lines, and vertical lines, as shown in FIGS. 11A and 11B . Because the polarity of data voltages can be inverted between successive frame periods, horizontal lines, and vertical lines, the dot inversion driving method is most commonly used within LCDs to minimize flickering.
- LCDs including the aforementioned Half V-Switching Mode FLC cells may be driven according to the dot inversion driving method. Accordingly, and with reference to FIGS. 11A and 11B , horizontally and vertically adjacent ones of Half V-Switching Mode FLC cells arranged within an LCD panel may alternately transmit and intercept light because each Half V-Switching Mode FLC cells can only transmit light in the presence of an applied electric field having a positive polarity.
- odd ones of the FLC cells arranged within odd horizontal lines of liquid crystal cells and even ones of the FLC cells arranged within even horizontal lines of liquid crystal cells transmit light in response to an electric field having a positive polarity (+) applied during odd frames (see FIG. 12A ) and intercept light in response to an electric field having a negative polarity ( ⁇ ) applied during even frames (see FIG. 12B ).
- even ones of the FLC cells arranged within odd horizontal lines of liquid crystal cells and odd ones of the FLC cells arranged within even horizontal lines of liquid crystal cells transmit light in response to an electric field having a positive polarity (+) applied during even frames (see FIG. 12B ) and intercept light in response to an electric field having a negative polarity ( ⁇ ) applied during odd frames (see FIG. 12A ).
- LCDs including a plurality of Half V-Switching Mode FLC cells may be driven according to the dot inversion driving method. Accordingly, and with reference to FIGS. 12A and 12B , horizontally and vertically adjacent ones of Half V-Switching Mode FLC cells arranged within an LCD panel may alternately transmit and intercept light because each Half V-Switching Mode FLC cells can only transmit light in the presence of an applied electric field having a positive polarity.
- odd ones of the FLC cells arranged within odd horizontal lines of liquid crystal cells and even ones of the FLC cells arranged within even horizontal lines of liquid crystal cells transmit light in response to an electric field having a positive polarity (+) applied during odd frames (see FIG. 12A ) and intercept light in response to an electric field having a negative polarity ( ⁇ ) applied during even frames (see FIG. 12B ).
- even ones of the FLC cells arranged within odd horizontal lines of liquid crystal cells and odd ones of the FLC cells arranged within even horizontal lines of liquid crystal cells transmit light in response to an electric field having a positive polarity (+) applied during even frames (see FIG. 12B ) and intercept light in response to an electric field having a negative polarity ( ⁇ ) applied during odd frames (see FIG. 12A ).
- reference numerals ‘P 1 ’ and ‘P 2 ’ indicate the polarization axes of polarization plates arranged on upper and lower substrates of the LCD panel, respectively.
- the polarization axis of each polarization plate determines polarization characteristics of light it will transmit.
- the polarization axes of the upper and lower polarization plates are substantially perpendicular to each other.
- liquid crystal cells transmitting light light having a polarization direction parallel to P 1 (or P 2 ) is transmitted by an incident polarization plate, through the FLC material, and is subsequently transmitted by a display polarization plate where the light transmitted by the display polarization plate has a polarization direction parallel to P 2 (or P 1 ).
- light having a polarization direction parallel to P 1 (or P 2 ) is transmitted by an incident polarization plate is not transmitted to the display polarization plate having the polarization axis of P 2 (or P 1 ).
- FIG. 13 illustrates a graph of a data voltage charged to a Half V-Switching Mode FLC cell within an LCD panel and the corresponding light transmissivity characteristics of the liquid crystal cell.
- a driving data voltage having a frequency of 60 Hz is uniformly applied to aforementioned FLC cells (e.g., FLC cells fabricated in the presence of an applied electric field having a negative polarity) arranged within the LCD panel. Accordingly, the polarity of the applied driving data voltage is inverted each successive frame period of the LCD panel (i.e., 16.7 ms).
- the FLC cells transmit light during odd frame periods 1Fr, 3Fr, 5Fr, etc., when the applied driving data voltage generates an electric field having a positive polarity (e.g., when the applied driving data voltage has a positive polarity, +V), and transmits substantially no light (i.e., intercepts light) when the applied driving data voltage generates an electric field having a negative polarity (e.g., when the applied driving data voltage has a negative polarity, ⁇ V). Therefore, when LCD panels including uniformly fabricated Half V-Switching Mode FLC cells are driven, the overall brightness of the LCD panel decreases and pictures displayed by the LCD panel appear to flicker because viewers perceive the transmitted light periodically within each frame period of the LCD panel.
- CRTs Cathode ray tubes
- CRTs are a type of impulse display system capable of displaying pictures instantaneously. Accordingly, the aforementioned blurring or contour trailing does not occur when moving pictures are displayed by CRTs.
- CRTs display pictures by irradiating electrons onto a portion of a fluorescent screen for short amount of time within each frame period. Accordingly, each portion of the fluorescent screen remains dark for a portion of each frame period.
- FIG. 14 CRTs display pictures by irradiating electrons onto a portion of a fluorescent screen for short amount of time within each frame period. Accordingly, each portion of the fluorescent screen remains dark for a portion of each frame period.
- LCDs display pictures by charging data voltages to liquid crystal cells during a scanning period when gate high voltages (Vgh) are applied, wherein, once they are charged, the data voltages are maintained within the liquid crystal cells until they are refreshed in a successive frame period.
- Vgh gate high voltages
- the present invention is directed to a ferroelectric liquid crystal display and method of driving the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
- An advantage of the present invention provides a ferroelectric LCD and a method of driving the same according to an impulse-type method wherein a voltage holding ratio (VHR) of liquid crystal cells is reduced.
- VHR voltage holding ratio
- the ferroelectric LCD may, for example, include a LCD panel having liquid crystal cells arranged in a matrix pattern, ferroelectric liquid crystal injected into the liquid crystal cells, gate lines, and data lines crossing the gate lines; a gate driving circuit for applying scan pulses at least twice to each gate line during one frame period of the LCD panel; and a data driving circuit for applying data voltages to the data lines of the LCD panel in synchrony with scan pulses.
- each liquid crystal cell may be provided as a Half V-Switching Mode FLC cell.
- the ferroelectric LCD may further include a timing controller for controlling the data driving circuit and the gate driving circuit.
- the timing controller may generate a multiple gate start pulse and apply the multiple gate start pulse to the gate driving circuit, wherein the multiple gate start pulse cause the gate driving circuit to sequentially generate scan pulses.
- the multiple gate start pulse may be generated at least twice during one frame period of the LCD panel.
- the data driving circuit may apply the same data voltages to data lines of the LCD panel at least twice during one frame period of the LCD panel.
- the data driving circuit may maintain a polarity of data voltages applied to the data lines of the LCD panel during one frame of the LCD panel.
- the data driving circuit may invert a polarity of the data voltages applied to the data lines of LCD panel at least twice during one frame period of the LCD panel.
- the timing controller may, for example, include a memory device for storing data so that the same data may be applied at least twice to the LCD panel during one frame period of the LCD panel.
- a driving method of the ferroelectric liquid crystal display may, for example, include applying a scan pulse to each gate line of a LCD panel at least twice during one frame period of the LCD panel, wherein the LCD panel is injected with FLC material; and applying data voltages to data lines of the LCD panel in synchrony with the scan pulses.
- FIG. 1 illustrates an equivalent circuit diagram of a related art active matrix liquid crystal display
- FIG. 2 illustrates a waveform diagram of scan pulses applied to gate lines of the liquid crystal display panel shown in FIG. 1 ;
- FIG. 3 illustrates an equivalent circuit diagram of a gate driving circuit for generating the scan pulses shown in FIG. 2 ;
- FIG. 4 illustrates a waveform diagram of the scan pulses shown in FIG. 2 and a data voltage supplied to a liquid crystal cell of a liquid crystal display panel in synchrony with the scan pulses;
- FIG. 5 illustrates a relationship between transmissivity of incident light and driving data voltages applied to V-Switching Mode ferroelectric liquid crystal cells
- FIG. 6 illustrates phase transformations of Half V-Switching Mode ferroelectric liquid crystal material
- FIG. 7 illustrates the fabrication of a liquid crystal cell including Half V-Switching Mode ferroelectric liquid crystal material
- FIGS. 8A and 8B illustrate a relationship between transmissivity of incident light and driving data voltages applied to V-Switching Mode ferroelectric liquid crystal cells aligned in the presence of applied electric fields having opposite polarities;
- FIGS. 9A and 9B illustrate an orientation of Half V-Switching Mode ferroelectric liquid crystal material aligned in the presence of an applied electric field and orientations of Half V-Switching Mode ferroelectric liquid crystal material driven in the presence of electric fields having polarities substantially identical to, and different from, the polarity of the applied electric field present during the alignment;
- FIG. 10 illustrates a waveform diagram of scan pulses shown in FIG. 2 and a data voltage supplied to a liquid crystal cell of Half V-Switching Mode in synchrony with the scan pulses;
- FIGS. 11A and 11B illustrate a dot inversion driving method of driving a liquid crystal display panel
- FIGS. 12A and 12B illustrate light transmission and interception characteristics of uniformly aligned Half V-Switching Mode ferroelectric liquid crystal cells driven in accordance with the dot inversion driving method
- FIG. 13 illustrates a graph of a driving data voltage charged to Half V-Switching Mode ferroelectric liquid crystal cells and light transmissivity characteristics of the liquid crystal cells corresponding to the charged driving data voltage;
- FIG. 14 illustrates light transmissivity characteristics of a cathode ray tube
- FIG. 15 illustrates light transmissivity characteristics of a related art liquid crystal display
- FIG. 16 illustrates a block diagram of a ferroelectric liquid crystal display according to the principles of the present invention
- FIG. 17 illustrates a cross-sectional view of liquid crystal cells arranged within two adjacent vertical lines of liquid crystal cells of a ferroelectric liquid crystal display in accordance with the principles of the present invention
- FIG. 18 illustrates a waveform diagram of a multiple gate start pulse applied to the gate driving circuit shown in FIG. 16 and scan pulses applied to gate lines of the liquid crystal display panel FIG. 16 in accordance with the multiple gate start pulse;
- FIG. 19 illustrates a waveform diagram of a scan pulse shown in FIG. 18 and a data voltage applied to a liquid crystal cell of a liquid crystal display panel in synchrony with the scan pulse;
- FIG. 20 illustrates a graph of a data voltage applied during driving of the liquid crystal cells shown in FIG. 17 and corresponding light transmissivity characteristics of the liquid crystal cells in accordance with the multiple gate start pulse of the present invention.
- FIG. 16 illustrates a driving apparatus of liquid crystal display according to the principles of the present invention.
- FIG. 17 illustrates a cross-sectional view of two adjacent liquid crystal cells of a ferroelectric liquid crystal display in accordance with the principles of the present invention.
- a liquid crystal display may, for example, include an LCD panel 64 having a plurality of Half V-Switching Mode FLC cells arranged in matrix pattern, a data driving circuit 62 for applying data voltages to data lines D 1 to Dm of LCD panel 64 , a gate driving circuit 63 for applying scan pulses to gate lines G 1 to Gn of LCD panel 64 , and a timing controller 61 for controlling the data and gate driving circuits 62 and 63 .
- the LCD panel 64 may, for example, include a TFT array substrate 70 and a color filter array substrate 72 coupled to, and spaced apart from, each other using a sealant (not shown).
- Ferroelectric liquid crystal (FLC) material may be injected between the TFT and color filter array substrates 70 and 72 , respectively.
- the TFT array substrate 70 may include first and second metallic layers deposited and patterned on a lower substrate 1 .
- the first metallic layer may be deposited and patterned to form a plurality of gate electrodes 2 protruding from respective ones of the gate lines G 1 to Gn. Accordingly, scan signals (e.g., gate high voltages) may be applied to gate electrodes 2 of each TFT via respective ones of the gate lines G 1 to Gn.
- the second metallic layer may be deposited and patterned to form a plurality of source electrodes 6 protruding from respective ones of the data lines D 1 to Dm and a plurality of drain electrodes 7 , spaced apart from respective ones of the plurality of source electrodes 6 .
- the plurality of drain electrodes may be connected to respective ones of subsequently formed pixel electrodes 9 within each liquid crystal cell.
- a gate insulating film 3 formed of an inorganic insulating material may be formed between the two patterned metallic layers and electrically insulate the first metallic layer from the second metallic layer.
- An active layer 4 and an ohmic contact layer 5 may be formed between the gate insulating film 3 and the source and drain electrodes 6 and 7 , to provide a channel between the source and drain electrodes of the TFT.
- the active layer 4 may be formed of intrinsic amorphous silicon material.
- the ohmic contact layer 5 may be formed of semiconductor material doped with n-type or p-type impurities.
- a protection layer 8 formed of an organic or inorganic insulating material may be formed over the entire surface of the lower substrate 1 , including the TFTs and the gate insulating film 3 .
- Pixel electrodes 9 may be formed to electrically connect with respective ones of the previously formed drain electrodes 7 through contact holes formed in predetermined regions of the protection layer 8 .
- a first alignment film 10 may be formed over the entire surface of the lower substrate 1 and may contact subsequently injected FLC material 11 .
- the surface of the first alignment film 10 that is contactable by the FLC material may include a plurality of grooves (not shown) for aligning molecules of liquid crystal material along a first alignment direction.
- a first polarization plate 17 may be mounted to the rear surface of lower substrate 1 for selectively transmitting light having a first linear polarization direction.
- the color filter array substrate 72 may include an upper substrate 12 supporting a black matrix 14 layer, wherein the black matrix layer 14 prevents light leakage at a boundary region between adjacent liquid crystal cells provided with liquid crystal material having undesirable optical transmittance properties.
- a color filter layer 13 may be provided over the black matrix layer 14 for selectively transmitting light having predetermined wavelength ranges corresponding to red, green, and blue colors.
- a common electrode 15 may be formed over the entire surface of the upper substrate 12 including the black matrix layer 14 and the color filter layer 13 .
- the common electrode 15 may be formed of a transparent conductive material.
- the common electrode 15 may be formed via a evaporation deposition technique or the like.
- a second alignment film 16 may be formed over the entire surface of the upper substrate 12 and may contact subsequently injected FLC material 11 .
- the surface of the second alignment film 16 that is contactable by the FLC material may include a plurality of grooves (not shown) for aligning molecules of liquid crystal material along a second alignment direction, substantially parallel to the first alignment direction.
- a second polarization plate 18 may be mounted to the front surface of the upper substrate 12 for selectively transmitting light having a second linear polarization direction.
- the first linear polarization direction and the second linear polarization direction may be substantially perpendicular.
- the FLC material 11 may be provided as Half V-Switching Mode FLC material.
- the FLC material may be injected at a temperature at which the FLC material exhibits an isotropic phase.
- the temperature of the injected FLC material exhibiting the isotropic phase may then be lowered below a first phase transformation temperature (Tni) such that the cooled injected FLC material exhibits a nematic phase (N*).
- Tni first phase transformation temperature
- N* nematic phase
- the temperature of the cooled FLC material exhibiting the nematic phase (N*) may be lowered below a second phase transformation temperature (Tsn) while applying an electric filed to the LCD panel sufficient to induce a spontaneous polarization of the FLC material.
- the FLC material may be aligned in correspondence with the applied electric field as the FLC material is cooled to exhibit a smectic C phase (Sm C*).
- a FLC material exhibiting the monostable state may be obtained.
- the injection temperature may be about 100° C.
- the first phase transformation temperature (Tni) may be about 90° C. to about 100° C.
- the second phase transformation temperature (Tsn) may be about 60° C. to about 80° C.
- the first and second transformation temperatures (Tni and Tsn, respectively) may vary according to the type of FLC material injected.
- the applied electric field may be generated by applying a voltage directly to upper and lower electrodes of the LCD panel.
- the applied electric field may be generated by applying a direct current voltage of about ⁇ 1-9V to the LCD panel.
- the applied electric field may have an alignment polarity pattern wherein a polarity of the electric field applied to the LCD panel may be inverted between vertical lines of liquid crystal cells within the LCD panel.
- the direction of the spontaneous polarization of the FLC material may be substantially identical to a direction of the applied electric field.
- the FLC material may be injected into the liquid crystal cells of the LCD panel at a temperature at which the liquid crystal material exhibits the nematic (N*) phase.
- the FLC material may be dispensed onto one of the substrates, rather than being injected between the two substrates. Accordingly, after the FLC material is dispensed onto one of the substrates, the other of the substrates on which the FLC material is not dispensed is bonded to the substrate having the dispensed FLC material.
- the data driving circuit 62 may invert the polarity of data voltages applied to the data lines D 1 to Dm (R, G, and B) between successive frames in response to a data control signal (DDC) outputted by the timing controller 61 . Further, the polarity of the data voltages applied to the consecutive ones of the data lines D 1 to Dm may be inverted. Therefore, and though not shown, the data driving circuit 62 may, for example, include a shift register, a data register, a first latch, a second latch, a digital-to-analog converter (DAC), and an output circuit connected in succession between the timing controller 61 and the data lines D 1 to Dm.
- DDC data control signal
- the shift register may generate a carry signal by shifting a source start pulse (SSP) and deliver the carry signal to a next stage shift register.
- SSP source start pulse
- the data register may temporarily store the digital pixel data (R, G, B) outputted by the timing controller 61 and supply the stored digital pixel data (R, G, B) to the first latch.
- the first latch may latch the digital pixel data (R, G, B) outputted by the data register in correspondence with one horizontal line and may output previously latched digital pixel data in correspondence with another horizontal line.
- the second latch may latch the data corresponding with the another horizontal line outputted from the first latch and output latched digital pixel data corresponding to yet another horizontal line in response to a source output enable (SOE) outputted by the timing controller 61 .
- SOE source output enable
- the DAC may decode the digital pixel data outputted by the second latch and select a positive gamma voltage or negative gamma voltage to correspond with the digital pixel data in response to a polarity control signal (POL) outputted from timing controller 61 .
- the polarity control signal (POL) may maintain a predetermined logic value of the polarity during the entire frame period of the LCD panel such that the polarity of the applied analog data voltage is not inverted during the frame period of the LCD panel.
- the polarity control signal (POL) may cause the polarity of the applied analog data voltage to be inverted at least once during the frame period of the LCD panel. Accordingly, the DAC may control the polarity of an analog data voltage applied to LCD panel 64 .
- the output circuit may be mounted between the DAC and the data lines D 1 to Dm and minimize a signal attenuation of data voltages supplied to the data lines D 1 to Dp, wherein p is a positive integer smaller than m.
- the gate driving circuit 63 may sequentially apply scan pulses at least twice to each gate line G 1 to Gn during a single frame period of the LCD panel 64 in response to a multiple gate start pulse (MGSP) and a gate control signal (GDC) outputted from the timing controller 61 . Accordingly, the sequentially applied scan signals may successively scan the horizontal lines of liquid crystal cells included within the entire LCD at least twice.
- the gate driving circuit 63 may, for example, include a shift register for generating scan pulses and a level shifter 92 for shifting the scan pulse voltages to the level appropriate to the drive the liquid crystal cell (CLc) in response to the multiple gate start pulse (MGSP) and the gate control signal (GDC).
- the timing controller 61 may, for example, generate a data control signal (DDC), a gate control signal (GDC), and a multiple gate start pulse (MGSP) in response to a vertical synchronization signal (V), a horizontal synchronization signal (H), and a main clock (MCLK) outputted from a main driving circuit board (not shown).
- the data control signal (DDC) may, for example, include a source start pulse (SSP), a source shift clock (SSC), a source output control signal (SOC), a polarity control signal (POL), and the like.
- the gate control signal may include, for example, include a gate shift clock (GSC), a gate output control signal (GOE), and the like.
- the timing controller 61 may sample the digital pixel data (R, G, B) inputted during a data enable period and supply the sampled digital pixel data (R, G, B) to the data driving circuit 62 in accordance with a one channel system.
- the timing controller 61 may divide the digital pixel data (R, G, B), inputted during the data enable period, into even data and odd data and supply the divided digital pixel data (R, G, B) to the data driving circuit 62 in accordance with a two channel system.
- the timing controller 61 may further include a memory device for storing the digital pixel data (R, G, B) during one frame period of the LCD panel.
- the memory device may be provided as a frame memory capable of storing digital pixel data for each liquid crystal cell within the entire LCD panel for one frame period of the LCD panel.
- the memory device may store the digital pixel data within a period of time smaller than one frame period of the LCD panel. After the digital pixel data is stored in the memory device, it may be applied to the data driving circuit 62 at least twice during one frame period of the LCD panel.
- FIG. 18 illustrates a waveform diagram of a multiple gate start pulse applied to the gate driving circuit shown in FIG. 16 and scan pulses applied to gate lines of the liquid crystal display panel FIG. 16 in accordance with the multiple gate start pulse.
- the period of the multiple gate start pulse (MGSP) may be half or less than half of the frame period of the LCD panel. Accordingly, and in one aspect of the present invention, the gate driving circuit 63 may sequentially apply the scan pulses SP 1 to SPn corresponding ones of the gate lines G 1 to Gn, respectively, every half frame period in response to the multiple gate start pulse (MGSP), also generated every half frame period.
- the pulse width of the multiple gate start pulse (MGSP) and the scan pulses SP 1 to SPn may be decreased proportionally (e.g., by about half) as compared with the pulse widths of scan pulses applied only once to the gate lines G 1 to Gn during one frame period of the LCD panel.
- FIG. 19 illustrates a waveform diagram of a scan pulse shown in FIG. 18 and a data voltage applied to a liquid crystal cell of a liquid crystal display panel in synchrony with the scan pulse.
- data voltages charged to the FLC cells of the ferroelectric LCD in accordance with the principles of the present invention may charge data having the same gray scale value and polarity twice during one frame period of the LCD panel in response to scan pulses applied in accordance with the multiple gate start pulse (MGSP). Accordingly, the average voltage (Vavrg) charged within the FLC cell during one frame period of the LCD panel becomes substantially identical to the peak data voltage (Vdata) of the data voltage applied to the FLC cells via data lines D 1 to Dn. Therefore, even though the FLC cells abruptly discharge the charged data voltages, the VHR is reduced compared to the VHR of the related art LCD. Thus, the brightness of the FLC cells increase along with the ability to control the gray scale values of the expressed images. Also shown in FIG. 19 , ‘Vgh’ designates a high logic voltage of the scan pulse (SP) and ‘Vgl’ designates a low logic voltage of the scan pulse (SP).
- FIG. 20 illustrates a graph of a data voltage applied during driving of the liquid crystal cells shown in FIG. 17 and corresponding light transmissivity characteristics of the liquid crystal cells in accordance with the multiple gate start pulse of the present invention.
- the polarity of the data voltages applied to the FLC cells may be inverted every half frame period of the LCD panel.
- the polarity of the applied data voltage may be inverted when a multiple gate start pulse is generated. Assuming the FLC cell is aligned in the presence of an applied electric field having a negative polarity, the FLC cell may transmit light in the presence of a driving data voltage having a positive polarity applied during a first half frame period of the LCD panel.
- the FLC cell described above may transmit substantially no light in the presence of a driving data voltage having a negative polarity applied during a second half frame period of the LCD panel, substantially equal to the remainder of the frame period of the LCD panel after the first half frame period has elapsed. Accordingly, the data voltages applied to the FLC cells have the same gray scale value while the polarity of the applied data voltages is inverted. Because identical data voltages having inverted polarities are applied to FLC cells during one frame period of the LCD panel, the flicker phenomenon is substantially negligible within the LCD according to the principles of the present invention as compared to related art LCDs.
- a gate start pulse may be generated at least twice during a single frame period of the LCD panel. Further, the polarity of identical data voltages may be maintained and applied to the LCD panel at least twice during the same frame period of the LCD panel. As a result, the voltage holding ratio (VHR) may be reduced (i.e., improved) and the brightness of the LCD panel and the ability to control gray scale vales of expressed images may be increased.
- VHR voltage holding ratio
- ferroelectric LCD and the method of driving the same may generate gate start pulses at least twice during one frame period of the LCD panel and invert the polarity of identical data voltages at least once during the same frame period of the LCD panel such that data voltages may be applied to the LCD panel at least twice during the same frame period of the LCD panel. Accordingly, the flicker phenomenon may be minimized.
- the gate start pulse may be generated twice during a single frame period (e.g., in accordance with half periods of the frame) by setting the width of the gate start pulse to less than half as compared with the widths of related art gate start pulses
- the gate start pulse of the present invention may be generated more than twice during one frame period of the LCD panel.
- the polarity control signal may cause the polarity of the data voltages to be inverted more than once during one frame period of the LCD panel.
- data voltages may be applied to the liquid crystal display panel more than twice during the same frame.
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KR1020020066582A KR100917323B1 (ko) | 2002-10-30 | 2002-10-30 | 강유전성 액정표시장치와 그 구동방법 |
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Cited By (4)
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US20090267885A1 (en) * | 2008-04-25 | 2009-10-29 | Himax Display, Inc. | Pixel circuitry and driving method thereof |
US20100259563A1 (en) * | 2005-11-29 | 2010-10-14 | Naoki Tokuda | Organic electroluminescent display device |
US20100309230A1 (en) * | 2009-06-08 | 2010-12-09 | Duck-Gu Cho | Light emitting device and method of driving the same |
US9187500B2 (en) | 2011-07-14 | 2015-11-17 | The Regents Of The University Of Colorado, A Body Corporate | Liquid crystal devices for information display and photonics applications |
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KR101012944B1 (ko) * | 2002-12-21 | 2011-02-08 | 엘지디스플레이 주식회사 | 강유전성 액정의 전계배향방법과 이를 이용한 액정표시장치 |
KR101061631B1 (ko) * | 2004-03-30 | 2011-09-01 | 엘지디스플레이 주식회사 | 액정표시장치의 구동장치 및 방법 |
TWI267054B (en) * | 2004-05-14 | 2006-11-21 | Hannstar Display Corp | Impulse driving method and apparatus for liquid crystal device |
CN100375145C (zh) * | 2004-11-08 | 2008-03-12 | 友达光电股份有限公司 | 单面板***整合的显示器 |
KR20060112474A (ko) * | 2005-04-27 | 2006-11-01 | 삼성전자주식회사 | 표시 장치 및 그 구동 방법 |
KR101409110B1 (ko) * | 2010-02-25 | 2014-06-17 | 샤프 가부시키가이샤 | 표시 장치 |
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Also Published As
Publication number | Publication date |
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KR100917323B1 (ko) | 2009-09-11 |
KR20040037901A (ko) | 2004-05-08 |
US20040085280A1 (en) | 2004-05-06 |
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